1. Field of the Invention
The present invention relates to composite shafts constructed from variable angle plies, or flags, such that the fiber orientation varies along the length of the shafts.
2. Description of the Related Art
Shafts made from non-metal materials, such as graphite composite, are routinely used with sporting equipment such as golf clubs. Composite shafts typically are constructed from multiple plies, or flags, of composite that are rolled onto a tapered mandrel in a process known as sheet wrapping. Each flag has a fixed fiber orientation relative to the longitudinal axis. In general, the fiber orientations used are 0°, which means the fibers run parallel to the shaft axis, ±45°, and 90°, which means that the fibers extend in a circumferential direction around the shaft.
A flag extends over a finite length along a shaft axis from a start position to an end position and is sized for a defined number of wraps about the shaft axis. As shown in FIG. 2, most flags are roughly trapezoidal in shape. A unidirectional composite material typically is comprised of fibers oriented along a given direction with resin matrix filler in a thin layer, which forms a configuration known as a prepreg. A prepreg also typically has a backing material to maintain integrity of the ply during handling.
For sheet wrapped construction, changing ply orientation along the length of the shaft requires that separate flags, oriented at different angles, be placed along the shaft axis. The flags are made to overlap in this construction to ensure structural continuity and strength. This overlapping configuration is detrimental, however, because it increases the complexity of the sheet wrapping process, adds weight, and creates an uneven thickness distribution in the wall of the shaft.
In view of the above, there is a need for thin, lightweight, composite shafts that are capable of resisting the stresses and strains placed upon them during use, particularly when they are used with golf club equipment.